1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements such as nails, bolts, pins and the like in a constructional component and including a combustion chamber for combusting an oxidant-fuel gas mixture and having an axially displaceable wall displaceable over at least one guide arranged in the combustion chamber by a press-on element, a guide cylinder adjoining the combustion chamber, and in which a setting piston is displaceably arranged for driving the fastening elements in the constructional component, and a gear drive operatively connecting the press-on element with the displaceable wall of the combustion chamber for displacing the displaceable wall in accordance with a transformation ratio between a press-on stroke and a displacement stroke of the displaceable wall.
2. Description of the Prior Art
Setting tools of the type described above are driven with gaseous or liquid fuels that are evaporated before combustion. The setting energy for driving in a fastening element is produced by combustion of a fuel-gas-oxidant mixture which fills the combustion chamber, and is transmitted to the fastening element by a setting piston. As an oxidant, e.g., oxygen from the surrounding air is used. Therefore, before each setting process. Fresh air should be brought into the combustion chamber, and after each setting process, the flue gas, which was produced by combustion of the oxidant-fuel gas mixture, should be removed from the combustion chamber.
In order to be able to effect a setting process, the setting tool should be pressed against a constructional component in order to prevent actuation of the setting tool in the absence of the contact of the setting tool with the constructional component. For ergonomical reasons, the press-on stroke should be as short as possible.
German Publication DE 40 32 203 A1 discloses a setting tool having a combustion chamber and a setting piston displaceable in a guide cylinder and driven by pressure generated as a result of combustion of an air-fuel mixture in the combustion chamber. The combustion chamber is located in a first housing part. The housing also has a second housing part displaceable relative to the first housing part. The guide cylinder is also displaceable relative to the combustion chamber. The guide cylinder is displaced by an intermediate rack and pinion gear as a result of the displacement of the second housing part relative to the first housing part. The displacement of the second housing part relative to the first housing part resulting from the setting tool being pressed against a constructional component, leads to displacement of the guide cylinder out of the combustion chamber, whereby the combustion chamber volume is increased.
In DE 40 32 203 A1, the combustion chamber is divided in several sub-chambers. The sub-chambers are separated from each other by at least one displaceable intermediate or separation plate displaceable together with the guide cylinder. For removal of the flue gas from the combustion space, the guide cylinder is displaced, together with the combustion chamber wall arranged thereon, back into the combustion chamber. This reduces the space of both sub-chambers to a minimum. The intermediate wall is displaced with the guide cylinder. As a result of the volume reduction of the sub-chambers, the flue gas is forced out of the combustion chamber. When the sub-chambers expand upon the setting tool being pressed against a constructional component again, they are again filled with fresh air.
The drawback of the setting tool described above consists in the complicated drive mechanics responsible for expansion of the combustion space of the combustion chamber.
In a setting tool Hilti GX 100 of the assignee herein, a bolt guide adjoins, in the drive-in direction, a piston guide in which a setting piston is displaceably arranged. A combustion chamber adjoins the piston guide at the end of the piston guide opposite the bolt guide. The combustion chamber has a rear wall displaceable along the axis of the combustion chamber. Upon the setting tool being pressed against a constructional component, the rear wall of the combustion chamber is displaced away from the piston guide up to an end of the combustion chamber remote from the piston guide, tensioning the return spring. The combustion chamber is in its expanded condition. Simultaneously with the expansion of the combustion chamber, it is filled with fresh air. The necessary press-on path is the same as the displacement path of the rear wall that corresponds to the axial length of the combustion chamber. After the completion of the setting process and lifting of the setting tool off the constructional component, the rear wall is displaced to its initial position by the biasing force of the return spring. The flue gases are forced out as the combustion chamber collapses. The advantage of this setting tool consists in that flushing is effected mechanically, and no batteries or accumulators are needed.
However, the above-described setting tool has a relatively long press-on path and a relatively large diameter of the combustion chamber.
European Patent EP 0 711 634 B1 discloses a combustion-engined setting tool having a combustion chamber in which an air-fuel gas mixture is combusted. Inside of the combustion chamber, there is provided ventilator means for generating turbulence. The ventilator means is driven by an electric motor which is supplied with an electrical energy from a battery. Because of the use of the ventilator means for flushing of the combustion chamber, the press-on path can be relatively short.
The drawbacks of the setting tool of EP 0 711 634 B1 consist in its large weight because of necessity in batteries or accumulators, and also in the need to replace them when their energy expires.
Accordingly, an object of the present invention to provide a setting tool of the type described above in which the drawbacks of the known setting tools are eliminated.